Tufting machines or similar systems for producing tufted articles such as carpets generally include one or more needle bars having a series of needles arranged in spaced series along their length. The needle bars typically are driven in a vertically reciprocating fashion by the operation of a main driveshaft of the tufting machine. As the main driveshaft is rotated, it drives a series of push rods linked thereto and which are connected to the needle bars. The needles carried by the needle bars thus are moved along a vertically reciprocating path or stroke into and out of a backing material passing through a tufting zone of the tufting machine. As the needles penetrate the backing material, each of the needles will carry a yarn therethrough and will be engaged by a loop pile looper, cut pile hook, level cut loop (LCL) looper, etc., so as to pick up and capture loops of yarns from the needles. Where cut pile hooks and/or LCL loopers are used, a series of knives further can be reciprocated into engagement with the cut pile hooks or LCL loopers so as to sever the loops of yarns captured thereon to form cut pile tufts.
When setting up a tufting machine, and further when changing styles or patterns of carpets being produced by the tufting machine, it can be necessary to change the stroke or amount of travel of the needles into and out of the backing material such as for adjustment of pile heights or other pattern effects. In addition, it also can be desirable to control the stroke or movement of the needles to provide for shorter or longer upstrokes of the needles such as to provide for increased dwell time that the needles remain out of the backing material during shifting of the needle bars. In the past, shims have been added as needed to adjust or change the position or elevation of the needles during changeovers and during initial set-up of a tufting machine to properly position the needles for a desired stroke. Adding such shims is, however, time consuming, requiring increased initial set-up time and labor for the set-up of the tufting machine, as well as during style/pattern change-overs, and requires the tufting machine to be shut down as these shims are added. The use of such shims further can limit the amount of adjustment provided.
Accordingly, it can be seen that a need exists for a system and method for variably driving the stroke of one or more needle bars in a tufting machine which addresses the foregoing and other related and unrelated problems in the art.